Safer polyvinylchloride with zero phthalate migration

Flexible polyvinylchloride (PVC) formulations are extensively used for the production of many different articles in the medical field, such as transfusion tubing and bags for blood or urine. They are further used for packaging purposes, toys, bathroom curtains, and kitchen floors. In order to obtain the desired flexibility, PVC has to be mixed with large amounts of plasticizers. Dioctyl phthalates (DOPs) are the most common additive used for this purpose. For thermodynamic reasons, these additives tend to migrate to the surface of an article. This leads to a progressive loss of its initial properties and also poses a serious health hazard when PVC articles for biomedical applications or children’s toys are used, because additives that have migrated to surface can contaminate physiological fluids such as blood, serum, or plasma. Exposure to phthalates has been shown to damage human tissues such as the pituitary gland, liver and testicles. Furthermore, the metabolic products of DOP are able to act as potential carcinogenic agents. As a result, several approaches have been developed to reduce plasticizer migration from flexible PVC to the environment. Some strategies require the surface modification of flexible PVC articles with peroxides, azides,1–3 sulfides4 or acrylates. Others involve physical treatments of the surface with gamma-radiation or plasma exposure.5–8 The most challenging strategy to solve any migration problems is to covalently bond the additive to the polymer chains. PVC can be chemically modified by nucleophilic substitution of its chlorine atoms by other compounds. Aromatic thiol compounds are the most efficient nucleophiles.9, 10 We have developed a synthetic route to functionalized plasticizers with physico-chemical properties similar to those of commercial DOP, but with an additional functional group able to establish a covalent bond to the polymeric backbone. We synthesized two novel functionalized phthalate additives: di(2-ethylhexyl) 4-mercaptophthalate (DOP-SH) and di-(2-ethylhexyl) 5-mercaptoisophthalate (isoDOP-SH) (see Figure 1). We carried out the modification reaction of PVC with the novel functionalized additives in two ways: either in solution or in aqueous suspension. In Figure 1. Chemical structures of the plasticizers described in the text.